The present invention generally relates to devices for projecting an image of a projection member, such as a transparency, through an optical system to form an apparent image thereof. More specifically, the present invention includes apparatus for altering or writing on the projection member by means of a writing light which is directed through the optical system in reverse fashion, and is focussed on a recording member disposed adjacent to the projection member.
For example, this invention allows an operator to use microfiche as a notebook which can accept additions and notations. This contrasts with the present situation in which it is difficult to overwrite new information on microfiche. This situation is as if printing had been developed, but the pen or pencil was as yet unknown.
This invention can also be applied to optical inspection and alteration of a workpiece under fabrication or repair.
The following U.S. Pat. Nos. are the most pertinent prior art known to the applicant: 3,892,965, 3,659,933, 3,650,612, 3,492,728, 3,480,965, 3,473,451, 3,915,567.
The prior art discloses several methods for marking or otherwise altering a projection member which is being viewed as an apparent image through an optical system. One such method uses a heated resistor which fuses and erases a portion of a microfilm frame. Other methods use styli which are driven to rub against a film surface and scrape the recorded information thereon from a local area thereof. Other methods employ flash tubes for pyrogenically altering a film transparency, or chemical means for etching a projection surface which creates an image. Other techniques involve super position of new and old informational images, so that the combined images may be rephotographed and stored.
All of these prior art methods suffer from serious disadvantages; they are either extremely expensive, or destructive of the projection member, or extremely cumbersome, or so time consuming that the value of the information added to the projection member is negated by the time required to record it.